Problem upgrading ZA Pro to 8.0.059 from 7.0.0483

Windows XP SP3
Even without ZA running (no launch on startup) and all AV disabled; I cannot get the install to run past 6%. The Event Viewer has this error:
Source:MsiInstaller Failed to connect to server. Error: 0x800706BA
Any fix? Note that I do not believe this is SP3 related, since I've run SP3 for a while now w/o issue.